1. Field of the Invention
The present invention is generally related to the illumination arts and is more particularly concerned with ornamental or decorative illumination of the sort that simulates a flame. A specific example is the electronic simulation of a torch of the sort commonly referred to as a garden torch or a tiki torch.
2. Background Information
Candles, and other flames, are sometimes simulated by electrically powered illumination sources. Notable among the patented prior art in this area are:
U.S. Pat. No. RE37,168, wherein St. Louis discloses an approach to simulating a flickering candle by using a single incandescent lamp driven by two oscillators having slightly different frequencies so as to provide electric drive pulses having varying widths.
U.S. Pat. No. 5,924,784, wherein Chliwnyj et al. teach the use of a microprocessor running a flame simulation program to control the intensity of individual members of an array of lighting devices by controlling the width of electric driving pulses. The approach used by Chliwnyj et al. requires an individual control output to each controlled device, which substantially increases the cost of driving a large array of lighting devices, as is of interest when simulating a torch or other large flame.
U.S. Pat. No. 5,097,180, wherein Ignon et al. teach the simulation of a flickering candle light by using a plurality of independent analog oscillators to modulate the power supplied to a single incandescent filament.
U.S. Pat. No. 4,870,325, wherein Kazar discloses a flame simulation apparatus in which the intensity of a parallel-connected array of LEDs is controlled by a pulse-width modulation scheme.
U.S. Pat. No. 4,510,556, wherein Johnson teaches the use of a digital shift register to create pseudo-random voltage pulse trains for driving a set of three vertically spaced incandescent lamps. The uppermost lamp in Johnson""s array is driven independently, while the two lower lamps are driven together.
In a preferred embodiment, a relatively large flame, such as one might find in a garden torch, is simulated by means of a two-dimensional array of light emitting diodes (LEDs) controlled by a flame simulation program running on a microprocessor. The relatively large number of LEDs required for simulating a large flame can lead to expensive and complex control arrangements if each LED is separately controlled. The flame simulation of the invention reduces the magnitude of this problem by arranging the individual LEDs into at least one two-dimensional array having some selected number, N, of columns and another selected number, M, of rows, where the matrix has the anodes of all the LEDs in one column (or row) connected in common to exactly one column buss, and the cathodes of all the LEDs in one row (or column) connected in common to exactly one row buss. The microprocessor acts to connect the vertically-oriented columns of the matrix to a source of electric power one at a time, and to then drive all of the rows by providing a multi-bit digitally encoded output to one or more digital-to-analog converters (D/A), each of which converts the encoded output to an analog voltage and that applies that voltage to a resistor ladder network connected to each horizontal row of LEDs in the matrix. The amplitude of the driving signal applied to any selected LED in a selected column of the matrix thus depends on both the voltage amplitude output by the D/A and the total value of electrical resistance due to the ladder network interposed between the D/A and the LED""s row.
The two-dimensional array used for flame simulation is preferably arranged so that it can be viewed from any horizontal direction. This may be done by arranging the array on the surface of an upstanding cylinder, or by using some selected number, preferably three or more, of flat arrays placed around a vertical axis so as to approximate a cylinder. It will be understood, moreover, that although the arrays described herein will be treated as comprising N columns with M LEDs in each column, one could make an array that served the same purpose but that had one or more columns having fewer than M rows. Arrangements of this sort provide for simulations with partially defective arrays, as well as simulations having a regular pattern of taller and shorter columns.
In preferred embodiments of the invention, although portions of the array are visible from any angle as a viewer walks around a simulative torch, some elements of the array are hidden from view regardless of the viewing position. If one considers a array comprising three subarrays disposed about a vertical axis, for example, at least one of the three subarrays will be hidden from view. In some such cases, there will be some number, n, of columns of light sources that are hidden, so that the viewer can see no more than Nxe2x88x92n columns. In control arrangement used with some embodiments of the invention this lack of total visibility is used to decrease the number of column drivers required. This may be done by driving multiple columns at the same time, where the columns are grouped (normally paired) so that only one of the columns in the group is visible from any one viewing angle. Alternately, one can interleave the times at which columns are selected so as to drive the kth column on one face and then the kth column on a second fact. Those skilled in the art will realize that it is also possible to simulate flames with a two dimensional array of elements, all of which are viewable from a single location. In such cases, n=0.
Although the preferred light source for practicing the invention is a LED, it will be understood that many other light sources, such as incandescent lamps, arc discharge lamps, electroluminescent emitters, etc. could equally well be used.
A preferred embodiment of the invention comprises electronic apparatus for simulating a flame. The apparatus comprises a selected number, greater than one, of light sources arranged as an array of N vertical columns and M horizontal rows in which no more than Nxe2x88x92n of the columns are visible from any one viewing location. Each of the light sources, which may be a LED, has two electrical terminals. A first electrical terminal of each of the M light sources in each column is electrically connected to a common output of a respective one of no more than Nxe2x88x92n drivers and the second electrical terminal of each light source is connected in common with the second electrical terminals of all the other light sources disposed in the same row, as well as to a respective point on a resistive ladder network. There is also at least one D/A converter that has an output connected to a point on the resistive ladder network at which none of the second electric terminals are connected. A controller, which is preferably a microprocessor, provides a binary encoded output comprising at least two separate bit outputs to each of the at least one D/A converters and also provides a separate output to each of the Nxe2x88x92n drivers. The total number of outputs from the controller is less than Nxc3x97M.
A preferred embodiment of the invention comprises apparatus for simulating a flame by sequentially controlling a respective intensity of illumination provided by each of a selected number, greater than one, of light sources arranged in a vertically extending array. Each of the light sources has the capability of providing a respective intensity of illumination responsive to an amplitude of a voltage applied across its terminals. The apparatus also includes a controller that can operate under control of a flame simulation program stored in its memory to supply at least one binary-encoded output value at one of a plurality of output connections. There is also at least one digital-to-analog converter for receiving a binary-encoded output from the controller and for converting that value to a corresponding analog voltage. This analog voltage output is connected to the light sources through an electrical resistance, which may be provided by a resistive ladder network. Hence, the amplitude of the voltage actually applied across each of the light sources is determined jointly by the amplitude of the analog output signal and the value of the respective electrical resistance.
Another aspect of the invention is that it provides a method of simulating a flame by controlling a plurality of electrically-powered illumination sources spaced out at a selected number of positions along at least one vertical line, where each of the illumination sources is adapted to provide an illumination intensity responsive to a voltage supplied one of its respective input terminals. This method comprises the steps of: using a program stored in a memory of a computer to generate a sequence of binary-encoded values, each of which is representative of a respective illumination intensity; supplying the sequence of binary encoded values to at least one digital to analog converter where the sequence is converted to a corresponding sequence of analog voltage values; and applying the sequence of analog voltages to an input of a resistor ladder network that has the same selected number of output connections, each of which is connected to an input terminal of at least one of the illumination sources.
Although it is believed that the foregoing recital of features and advantages may be of use to one who is skilled in the art and who wishes to learn how to practice the invention, it will be recognized that the foregoing recital is not intended to list all of the features and advantages. Moreover, it may be noted that various embodiments of the invention may provide various combinations of the hereinbefore recited features and advantages of the invention, and that less than all of the recited features and advantages may be provided by some embodiments.